This invention relates to a storage system. More specifically, this invention relates to a storage system comprises a storage controller such as a disk array controller, which stores data in one or more disk drives, a tape library controller, an optical disk library controller, a solid-state disk controller (e.g., semiconductor disk controller), or a storage controller that uses a non-volatile memory, typically, flash memory.
Companies and public offices store an increasing amount of digital data recording personal information, and now those who let such information leak have to face legal consequences. It is therefore an urgent task for any organization that keeps personal information and other digital data to make sure that the information is managed securely and is protected against the risk of leakage.
A common technique that is currently available for this task is to encrypt data in a storage system by using an appliance-type encryptor in conjunction with a storage controller (see “Securing Networked Storage whitepaper”, DECRU Inc., 2004 and US 2004/0153642 A).
With data in a storage system encrypted by this method, it is difficult for a person who obtains the storage system, or a magnetic disk drive (HDD) mounted to the storage system, through theft or other illegal measures to decode the data.
Also known are a volume mirror function, with which different logical volumes in a storage system share the same data, and a snapshot function (see “Data Protection with Storage Networks Part II”, pp. 25 to 45, [online], 2004, SNIA, Internet <URL:http://www.snia.org/education/tutorials/fall2004/backup/data_protection_partII.pdf> and “Examination of Disk-based Data Protection Technologies”, pp. 23 to 36, [online], 2005, SNIA, Internet <URL:http://www.snia.org/education/tutorials/spr2005/datamanagement/ExaminationofDiskBasedDataProtection-v5.pdf>).
There is also a write operation called write after and employed to write in a cache memory as well as in a disk drive. A specific example can be found in a scalable storage system of JP 07-20994 A. This storage system has plural host adapters, which are connected to an upstream CPU, plural disk adapters, which are connected to array disks, and a short-term cache memory, which is shared among the adapters. The adapters and the cache memory are detachably attached to a common bus, which is shared among the adapters and the cache memory. The scale of the storage system is enlarged by merely adding as many adapters and cache memories as necessary. The adapters, cache memory, and the common bus are duplicated to enable the storage system run in a degenerate mode in the event of a failure. The adapters and the cache memory can be hot plugged in and out of the common bus, thereby making it possible to perform maintenance work and replace parts without shutting down the storage system.